Apparatus for mixing explosive materials and for filling of ordnance

ABSTRACT

Described herein is apparatus for the mixing of explosive materials utilising a static mixer ( 26 ) for combining pre-mix explosive material and hardener prior to introducing the combined mixture into any ordnance ( 38 ).

This invention relates to the field of the filling of ordnance withexplosive materials, and more specifically to the use of static mixingin the filling process.

Traditional methods used for filling ordnance with polymer bondedexplosive (PBX) utilise a filling process based on the combination ofusually two materials, namely an explosive mixture (pre-mix) andhardener, which are mixed together immediately prior to use in fillingthe chosen ordnance.

In a typical application of the mixing and filling process, a pre-mix ofexplosive such as for example PBX is produced and typically mixed with ahardener (i.e. IPDI) the combined mixture being mixed together in a highshear mixer.

Once mixed, the bowl of the high shear mixer containing the fully mixedPBX composition is fitted with a pressure plate apparatus and cover,then raised to an appropriate filling height on a specialised bowl lift.

Once elevated into position, the bowl of fully mixed PBX composition ispressurised using an inert gas (i.e. nitrogen) for the purposes ofaiding the dispensing of the fully mixed PBX composition through asystem of pipes to the ordnance filling position.

Ordnance to be filled is typically placed in a vacuum chamber and afilling attachment from the bottom outlet valve of the mixer bowlcontaining the fully mixed PBX composition is attached to the chamber.Typically the vacuum will be evacuated to <100 millibars.

The vacuum provides the physical motivation for the fully mixed PBXcomposition to flow into the ordnance when the valve from the bottomoutlet of the mixer bowl is released. The quantity of fully mixed PBXcomposition introduced to the cavity within the ordnance is usuallyjudged visually, and when sufficiently filled the vacuum to the chamberis released and the filled component removed ready for the introductionof the next ordnance component to be filled.

The traditional method of filling ordnance as described above suffersfrom a number of problems associated with the finite ‘pot life’ time ofthe fully mixed PBX composition and the fact that once the variouschemicals have been combined the ‘pot life’ time defines the periodwithin which the filling process must be completed before the PBXcomposition cures and can no longer be used in the process (i.e. wouldsolidify within the pipe work).

The ‘pot life’ is typically in the order of two hours and in instanceswhere there are no problems associated with a particular batch ofcomponents, then the mixing of PBX and hardener (IPDI) in a bowl and thesubsequent dispensing of the fully mixed PBX composition into ordnancecan be achieved relatively quickly. However, if for any reason (forexample mechanical breakdown etc) the filling process has to beinterrupted or indeed suspended, then the whole of the fully mixed PBXcomposition has to be purged from the mixing and filling apparatus, thepurged material being lost to waste.

The invention described herein provides for apparatus and a method forthe mixing of explosive compositions and the subsequent filling ofordnance without being subject to the problems associated with having tomix and use a specific quantity of explosive composition within alimited ‘pot life’ period.

Accordingly there is provided apparatus for the mixing of explosivematerials, comprising:

-   -   a reservoir of pre-mixed explosive material,    -   a reservoir of hardener material,    -   a static mixer means,    -   each of said reservoirs having pipe means for conveying said        pre-mix explosive material and hardener material respectively        into the inlet of a static mixer means, the outlet of said        static mixer means being connected to means for effecting the        filling of ordnance components.

Preferably the pipe means for conveying each of said materials are notlinked or combined until they reach the inlet of said static mixermeans.

Preferably the means for filling each of said ordnance components withsaid final mixed explosive material will be controlled such that therespective pre-mix explosive material and the hardener materials areintroduced to the static mixer means on demand, thereby minimising theamount of combined explosive material in said apparatus to thatcontained in the static mixer means itself and the associated pipe-workused to connect the output of said static mixer unit to the ordnance forfilling.

The invention is now described by way of example only with reference tothe following drawing in which FIG. 1 is a diagrammatic representationof an explosive mixing and ordnance filling apparatus in accordance withthe invention.

FIG. 1 shows a pre-mix explosive material 2 is shown in a high shearmixing bowl assembly 4 wherein the mixing of the pre-mix explosivematerial 2 has been completed, the pre-mix explosive material 2 beingheld within the mixing bowl 4 subjected to controlled pressure by theaction of a hydraulic cylinder 6 and ram 8 assembly. Hydraulic cylindercontrol means 10 is shown for controlling the flow of pre-mix explosivematerial 2 through the exit valve 12 and onwards through the pre-mixexplosive material pipe work 14.

Hardener material 16 is depicted housed within a header tank 18 havingpipe work 20 leading to a pump means 22 to provide the controlled supplyof hardener material 16 through the pipe work 24.

A static mixer means 26 is provided having pipe work 14 and 24 at itsinlet port 28 and an outlet port 30 and corresponding pipe work 32 forconveying final mixed explosive material 34 to ordnance filling stations36.

In use, ordnance 38 to be filled with final mixed explosive composition34 are positioned at ordnance filling stations 36. When the ordnance iscorrectly in position 38 and the associated fill-to-level controlapparatus is connected (not shown). A signal from the process control 40to initiate the filling operation is activated. A demand signal isreceived by the fill-to-level controller 42 from the non-contact levelsensor 46 indicating that the ordnance is not filled and accordingly thefill-to-level controller 42 sends a demand signal to the pre-mixexplosive material hydraulic cylinder controller 10 and the hardenermaterial pump 22.

The pre-mix explosive material 2 and hardener material 16 are conveyedthrough their respective separate pipe works 12, 24, both materials 2,16 being introduced individually to the inlet 28 of the static mixermeans 26. It is important to note at this point that in accordance withthe invention the point at which the pre-mix explosive material 2 andhardener material 16 are first combined is substantially at the inletport 28 of the static mixer means 26 thereby providing a distinguishingfeature over the prior art in which the two materials are normallycombined in the mixing bowl, thereby starting the ‘pot life’ for thecombined explosive material within the mixing bowl 4.

At the inlet 28 of the static mixer means 26 the pre-mix explosivematerial 2 and hardener material 16 are forced through a number ofstatic mixing blade means 4, thereby mixing the two materials 2, 16together. Such static mixing means are known within the confectioneryand food industries and typically comprise a plurality of blade meansarranged in a ‘corkscrew’ type manner which promotes the effectivemixing together of two or more materials when forced through the mixer.

Additionally, the use of a static mixing means provides for simplifiedcleaning of the apparatus following the completion of an ordnancefilling run, thereby further reducing the inherent complexity and timerequired for purging and cleaning using state of the art apparatus.

The combined final explosive mixture 34 passes through the static mixermeans exit port 30 and along the pipe-work 32 arriving at the ordnancefilling stations 36. At the filling stations 36 the flow of combinedexplosive mixture 34 into the waiting ordnance 38 is controlled viapinch valves 44, the operation of said pinch valves 44 being controlledso as to limit the volume of combined final explosive mixture 34introduced into the ordnance 38. A vacuum source 48 is provided toencourage the filling of the volume within the ordnance.

The control of the valves 44 (typically pinch valves) to enable theaccurate filling of the ordnance may be effected either by a humanoperator directly controlling a valve 44 or by a mechanised system,which for the purposes of this specific embodiment utilises anon-contact level controller 46 which forms part of an integratedcontrol system 10, 40, 42, 46, 48.

When the non-contact level controller 46 senses that ordnance 38requires filling with combined final explosive mix 34, then a signal issent to the fill-to-level controller 42 which in turn initiates the flowof both pre-mix explosive material 2 and hardener material 16 throughthe static mixing means 42 and via the outlet pipe work into the waitingordnance 38. When the non-contact level controller 46 senses that any ofthe ordnance 38 has reached its fill limit, then a signal is sent to thefill-to-level controller 2 to stop the flow of materials 2 and 16.

The non-contact level controller 46 may comprise an optical sensor, afibre optic sensor, a laser sensor or an LED sensor.

Using the above stated control means thereby provides for both apparatusand a method of filling ordnance 38 with combined final explosivemixture 34 in a controlled manner, utilising apparatus that prolongs the‘pot life’ of said combined final explosive material 34. This resultingin significantly less waste explosive material to be disposed of andadditionally simplifies the cleaning of the system by minimising thenumber of elements of the apparatus actually exposed to combined finalexplosive material 34. The method of filling ordnance 38 using suchapparatus and control means can provide an automated ordnance fillingsystem.

In order to clean the apparatus as described, the action of pumpingpre-mix explosive material 2 (or an alternative compatible inertmaterial) through the apparatus in the absence of any hardener material16 will be substantially sufficient to purge the system of any combinedfinal explosive material 34, thereby reducing the complexity, time anddanger level associated with purging state of the art apparatus withinwhich combined final explosive material has been allowed to cure.

In addition to the elements described in the specific embodiment of theinvention, a number of measuring sensors and safety devices would alsobe incorporated into the apparatus as shown in FIG. 1, namely a flowmeter sensor 50, a pressure sensor 52, temperature probes 56, a pressureswitch 58 and a safety burst disc 60. Such sensors and safety devicesare known in the art and are included in the specific embodiment by wayof example to illustrate the industrial application of the invention.

Additionally, a colour agent or dye can be added to the hardenermaterial 16 such that it will be possible to monitor the amount ofhardener 16 present in the final combined explosive mixture 34. Theanalysis of the colour of the combined mixture 34 may be made byutilising a colour sensor means located after the mixing processcalibrated to recognise particular ranges of colour as indicatingsufficient percentage of hardener in the combined material 34, or by useof a viewing window in the pipe work containing the combined mixture 34to allow for visual inspection of the colour of said mixture 34.

It is to be noted that the hydraulic cylinder 6 and ram 8 assembly isfar safer than using displacement pumps to pump the pre-mix explosivematerial to the static mixer 26. It is also to be noted that the pre-mixexplosive material is not pumped to the static mixer as this may be toodangerous.

As an alternative to the flow meter 50 being located in the pre-mixexplosive material pipe work 14, the flow meter may be located in thehydraulic line to the hydraulic ram 8. In this case, the flow meteraccurately measures the displacement of the ram 8 and hence the massflow of the pre-mix explosive mixture. This alternative is of particularuse when the pre-mix explosive material is too viscous and inaccurateflow readings are obtained when the flow meter is in the pre-mixexplosive material pipe work 14.

Other advantages of the invention will be readily apparent to thoseskilled in the art and the substitution of elements for mechanicalequivalents and adaptation of the process using different materials andthe like should be construed as being comprised within in the inventiveconcept as claimed.

References to ordnance in the above specification and claims shall beconstrued as non-limiting and in respect of the invention shall includewithout limitation shells, mortars, rockets, projectiles and any otherordnance or containers which are required to be filled with a combinedfinal explosive mixture.

1. Apparatus for the mixing of explosive materials, comprising: areservoir of pre-mixed explosive material, a reservoir of hardenermaterial, a static mixer means, each of said reservoirs having separatepipe means for conveying said pre-cure explosive material and hardenermaterial respectively to a static mixer means.
 2. Apparatus for themixing of explosive materials in accordance with claim 1, wherein saidmaterials are combined substantially at the inlet of said static mixermeans.
 3. Apparatus for the mixing of explosive materials in accordancewith claim 1, wherein the outlet of said static mixer means is connectedto means for effecting the filling of ordnance.
 4. Apparatus for themixing of explosive materials in accordance with claim 1 wherein themeans for filling each of said ordnance components with said combinedfinal explosive material is controlled such that the respective pre-mixexplosive material and hardener materials are introduced to the staticmixer means on demand, the demand controlled by an automated ordnancefill level control means.
 5. Apparatus for the mixing of explosivematerials in accordance with claim 1 wherein said fill-to-level controlmeans comprises at least one fiber optic sensor.
 6. A method for themixing of explosive materials utilizing apparatus in accordance withclaim
 1. 7. A method for the mixing of explosive materials in accordancewith claim 6, wherein the output from said static mixer is connected toapparatus for the filling of ordnance with explosive materials. 8-9.(canceled)